It is desirable in motor vehicles to provide a manually shifted transmission where clutching is accomplished by a hydraulically operated clutch rather than a manually actuated foot pedal type clutch. Ideally such a clutch could be coupled with engine sensors to provide desirable features found in automatic transmissions such as holding the vehicle on hills while allowing manual shifting of the clutch.
Conventional designs of a solenoid combined with a spool valve to control hydraulic actuation of a clutch were found to be lacking. Specifically, it was found that when supplying control fluid to the clutch, a transient flow of force developed which tended to be additive with the solenoid force. This caused overshooting of target control movements that can hinder consistency and stability in clutch control. Additionally, other known designs included contamination sensitivity due to extremely small dampening pilot ports. While such orifices have successfully demonstrated their use in cleaner environments, in the environment of a manual transmission clutch small control orifices were problematic due to the minute amounts of contaminants in the transmission fluid.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the invention.